Bondhead lead clamp apparatus and method

ABSTRACT

A method of forming improved wire bonds between the contact pads on semiconductor devices and individual lead frame fingers of a lead frame. The method includes the use of an individual independent lead finger clamp during the wire bonding process to provide increased stability of the individual lead finger for improved bonding. If desired, the method also provides for the use of a conventional fixed clamp for the lead fingers during the wire bonding process in addition to the individual independent lead finger clamp during the wire bonding process to provide increased stability of the individual lead finger for improved bonding and also provides for the replacement of the fixed clamp with another, or second, independent clamp.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/941,019,filed Aug. 28, 2001, now U.S. Pat. No. 6,435,400, issued Aug. 20, 2002,which is a continuation of application Ser. No. 09/407,483, filed Sep.28, 1999, now U.S. Pat. No. 6,325,275, issued Dec. 4, 2001, which is acontinuation of application Ser. No. 08/865,911, filed May 30, 1997, nowU.S. Pat. No. 6,000,599, issued Dec. 14, 1999, which is a continuationof application Ser. No. 08/597,616, filed Feb. 6, 1996, now U.S. Pat.No. 5,647,528, issued Jul. 15, 1997.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to forming wire bonds between thecontact pads on semiconductor devices and individual lead frame fingersof a lead frame.

More specifically, the present invention is related to the apparatus andmethod of forming improved wire bonds between the contact pads onsemiconductor devices and individual lead frame fingers of a lead frameusing one or more independently actuated bondhead lead clamps during thebonding process.

2. State of the Art

Well known types of semiconductor chip devices are connected to acomponent known as lead frames and subsequently encapsulated in plasticfor use in a wide variety of applications. The lead frame is typicallyformed from a single continuous sheet of metal, typically by metalstamping operations. The lead frame includes an outer supporting frame,a central semiconductor chip supporting pad and a plurality of leadfingers, each lead finger having, in turn, a terminal bonding portionnear the central chip supporting pad. Ultimately, the outer supportingframe of the lead frame is removed after the wire bonds between thecontact pads of the semiconductor chip device and the lead fingers aremade.

Since the lead frames are formed continuously using stamping operations,they are typically continuously rolled on a suitable reel and providedfor use. Such reeling operations of the lead frames cause the leadframes to have induced deformations therein leading to lead framesexhibiting longitudinal curvature and transverse curvature. Such leadframe curvature and any attendant deformation of the lead frame causeproblems in the formation of reliable wire bonds with the contact padsof semiconductor devices and the individual lead fingers of the leadframe, particularly, when the size of the semiconductor is decreased,the number of contacts pads on the semiconductor device is increased,and the number of lead fingers on the lead frame is increased.

Typical apparatus and methods for forming the wire bonds between thecontact pads on semiconductor devices and the lead fingers of leadframes are illustrated in U.S. Pat. Nos. 4,361,261, 4,527,730,4,600,138, 4,653,681, 4,765,531, and 5,465,899. However, such apparatusand methods do not address the problem of deformed lead frames and theireffect on the wire bonds.

Typically, the deformation of the lead frames and its effect on thequality of wire bonds have been dealt with through the use of clamps onportions of the lead frames during the wire bonding operation. In U.S.Pat. No. 4,434,347, a circular fixed clamp is used to retain the leadfingers of the lead frame during the wire bonding operation. A springloaded electrode is used to heat the end of the lead finger to helpimprove bonding of the wire.

In U.S. Pat. No. 5,322,207, a fixed clamp is used to retain the leadframe during the automated wire bonding process for connecting the bondpads of a semiconductor device to lead fingers of a lead frame.

In U.S. Pat. No. 5,307,978, a fixed clamp is illustrated for use in anapparatus and method for orienting bonding sites of a lead frame havinga plurality of bonding sites.

In U.S. Pat. No. 5,035,034, a hold-down clamp having a multi-fingeredinterchangeable insert for wire bonding semiconductor lead frames isillustrated. The clamp insert 21 includes a plurality of individualfingers 22 to be used to bias a lead finger of a lead frame in the wirebonding process to provide a better wire bond.

In U.S. Pat. No. 3,685,137, jaws 26 and 28 of a lead frame clamp areused to force the lead fingers of a lead frame into a fixed positionduring the wire bonding process.

In U.S. Pat. No. 4,821,945, a method and apparatus for the single leadautomated clamping and bonding of lead fingers of lead frames areillustrated. However, such apparatus and method are used to replace thefixed clamp during such wire bonding. Additionally, the individual clampis concentrically located with respect to the wire bonding apparatus andmust rotate therearound during wire bonding operations.

While such prior art apparatus and methods have been directed inattempting to solve the problems of forming reliable wire bonds betweenthe contact pads of semiconductor devices and lead fingers of leadframes, they have not been as successful as envisioned.

The present invention is directed to an improved wire bonding apparatusand method for forming such wire bonds.

SUMMARY OF THE INVENTION

The present invention is related to the apparatus and method of formingimproved wire bonds between the contact pads on semiconductor devicesand individual lead frame fingers of a lead frame. The present inventionincludes the use of an individual independent lead finger clamp duringthe wire bonding process to provide increased stability of theindividual lead finger for improved bonding. If desired, the presentinvention also provides for the use of a conventional fixed clamp forthe lead fingers during the wire bonding process in addition to theindividual independent lead finger clamp to provide increased stabilityof the individual lead finger for improved bonding. The presentinvention also contemplates the replacement of the fixed clamp withanother, or second, independent clamp in addition to the firstindividual independent lead finger clamp during the wire bondingprocess.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention will be better understood when the description ofthe invention is taken in conjunction with the drawings wherein:

FIG. 1 is a perspective view of the present invention used in a wirebonding process.

FIG. 2 is a perspective view of a lead-over-chip semiconductor devicehaving the bond pads thereof connected to the lead fingers of a leadframe.

FIG. 3 is a side view of the present invention used in the wire bondingof a semiconductor chip arrangement.

FIG. 4 is a perspective view of a second alternative type of independentlead clamp of the present invention.

FIG. 5 is a perspective view of a third alternative type of independentlead clamp of the present invention.

FIG. 6 is a perspective view of the use of two independent lead clampsof the present invention in a wire bonding operation with a lead fingerof a lead frame.

DETAILED DESCRIPTION OF THE INVENTION

Referring to drawing FIG. 1, a semiconductor chip (die) 10 is shownbeing supported by the paddle 12 of a lead frame. A heat block 20 isused to heat the paddle 12, die 10, and lead fingers 14 during the wirebonding process. As shown, a suitable wire 16 has one end thereof 17bonded to a bond pad of the die 10. The wire 16 may be of any suitabletype for connection and bonding purposes, such as gold, gold alloy,aluminum, aluminum alloy, etc. The other end 18 of the wire 16 is shownbeing bonded to the end 15 of a lead finger 14 of the lead frame by asuitable bonding apparatus 26. The bonding apparatus 26 may be of anysuitable type well known in the bonding area, such as a taillessthermosonic or ultrasonic capillary type bonding apparatus whichdispenses wire during the bonding process. As previously stated, thelead finger 14 is in contact with the heat block 20 to heat the leadfinger 14 to a suitable temperature for the bonding operation to helpinsure a satisfactory wire bond. If desired, in the wire bondingoperation, further shown in contact with lead finger 14 is a portion ofa conventional clamp 22 used to clamp portions of the lead frame duringsuch bonding operations. The clamp 22 may be of any well known suitabletype, such as those described hereinbefore, and is generic in shape.Further shown in drawing FIG. 1 is independently actuated lead clamp 24used in place of or in addition to the conventional clamp 22 to maintainthe lead finger 14 in position during the bonding process. Theindependent clamp 24 helps insure that the lead finger is in contactwith the heat block 20 during the bonding process and helps minimize anydeflection of the end 15 of the lead finger 14 so that the bondingapparatus 26 accurately, precisely contacts the end 15 to provide thedesired wire bond. The action of independent clamp 24, and if desiredthe additional use of fixed clamp 22, provides improved clamping of alead finger 14 during the wire bonding process as well as insures thatthe lead finger 14 is in intimate contact with the heat block 20 foreffectiveness.

During the wire bonding process, it is desirable for the heat block tobe heated to substantially 230 degrees Centigrade. Although the heatblock may be any suitable temperature during the bonding operation, theheat block 20 temperature should not exceed 300 degrees Centigrade toprevent thermal damage to the die 10. It is further preferred that thebond of the end 18 of the wire 16 made to the end 15 of the lead finger14 be made at a temperature of substantially 190 degrees Centigrade forbonding effectiveness. It is also preferred that the bonding apparatusexert a bonding force of substantially 50 to 100 grams when bonding theend 18 of the wire 16 to the end 15 of lead finger 14 for effective bondformation of the wire 16 to lead finger 14.

The independent clamp 24 may be of any suitable shape for use inindependently clamping the lead finger 14, in place of the use ofconventional fixed clamp 22, such as square, semicircular, rectangular,arcuate, etc. Also, as shown, the independent clamp 24 may beresiliently mounted through the use of a shoulder 50 thereon abutting aspring 52 to control the amount of the force exerted on any lead finger14 during the wire bonding operation. If desired, the independent clamp24 may include insulation or cushioning 25 on the end thereof. Theindependent clamp 24 is actuated independently of bonding apparatus 26and has the capability of independent movement along the x-axis, y-axisand z-axis with respect to the bonding apparatus 26. The independentclamp 24 is also free to move about the bonding apparatus 26 and thecentral axis of the die 10 so that any lead finger 14 that is to beconnected to bond pads on the die 10, regardless of location, may beaccommodated. The independent clamp 24 does not need to be, andpreferably is not, concentrically centered about the bonding apparatus26 so that it will not interfere with the operation thereof. Any desirednumber of independent clamps 24 may be used about the bonding apparatusto minimize the amount of movement of the independent clamp 24 betweenwire bonding operations. The independent clamps 24 may be located inquadrants about the die 10, or in any manner as desired.

Referring to drawing FIG. 2, a lead over chip configuration using thepresent invention is shown. The lead fingers 14 are located over thechip (die) 10 for wire bonding thereto. In such a configuration, thelead fingers 14 are secured to the die 10 by insulating adhesive strips30. During the bond operation, one or more of the independent clamp 24clamps the end 15 of lead finger 14 prior to the bonding of a wire 16thereto by one or more of the bonding apparatus 26. The independentclamp 24 applies sufficient pressure to the end 15 of the lead finger 14to compress the insulating adhesive strips 30 to insure a satisfactorybond between the end of any wire 16 and the end 15 of the lead finger14.

Referring to drawing FIG. 3, a die 10 is shown having a plurality ofwires 16 bonded thereto. As shown, one or more of the independent clamps24 contacts the end 15 of lead finger 14 aft of the area of the wire end18 to the lead finger 14. The bonds of the wire end 18 to the end 15 ofthe lead finger 14 are typically a wedge type wire bond, although a ballbond may be made if desired. As shown, the heat block 20 is in contactwith the paddle 12 of the lead frame and the lead fingers 14.

Referring to drawing FIG. 4, a portion of a lead finger 14 is shown inconjunction with a bonding apparatus 26 and modified independent leadclamp 22′. The independent lead clamp 22′ is formed having a modifiedend or foot 23 thereon to provide a larger clamping area of the clamp22′ on the end 15 of the lead finger 14 during bonding operations. Themodified end or foot 23 is substantially the same width as the leadfinger 14 and may be mounted to have articulated movement about the endof the independent clamp 22′ such as using a pin 125 extending throughsuitable apertures in a pair of ears 27 attached to the foot 23 and theend of the modified independent clamp 22′ for illustration purposes.

Referring to drawing FIG. 5, an independent clamp 22′ is shown having amodified end or foot 23′ located on the end thereof. The end or foot 23′may be integrally attached to the clamp 22′ or may have an articulatedmounting arrangement, such as shown in drawing FIG. 4. In this instance,the modified end or foot 23′ is generally semicircular, or arcuate, inconfiguration so as to engage a large portion of the end 15 of the leadfinger 14 surrounding the bonding apparatus 26 during the wire bondingoperation to hold the end 15 in position.

Referring to drawing FIG. 6, the independent clamp 24 is shown inrelation to the bonding apparatus 26 on the end 15 of a lead finger 14as well as further being shown in relation to a second independentlyactuated clamp 150 located thereon during wire bonding operations. Thesecond independently actuated clamp 150 may be of any suitable type andstructure such as described and illustrated hereinbefore. The clamp 24and second clamp 150 may be actuated independently of each other andindependently of the bonding apparatus 26 as described and illustratedhereinbefore.

METHOD OF BONDING

Referring to drawing FIGS. 1 through 3, in the method of the presentinvention, a die 10 is positioned within the bonding area of the bondingapparatus 26. If desired, for use in addition to an individualindependent clamp 24, a conventional clamp 22 serves to help straightenthe lead frame and position the lead fingers 14 during subsequentbonding operations. Next, the die 10 and the lead finger 14 are heatedto the desired temperature before bonding operations by the heater block20. At this time, the independent clamp 24 is engaged, moved to theappropriate lead finger 14 which is to have a wire bonded thereto, andthe clamp 24 actuated to clamp the end 15 of the lead finger 14 againstthe heat block 20 or the adhesive strip 30. The wire bonding apparatus26 is then actuated to form a wire bond on end 17 of wire 16 to anappropriate bond pad on die 10. After the formation of the bond of end17 of wire 16 to the bond pad of die 10, the bonding apparatus is movedto appropriate end 15 of lead finger 14 for the formation of a suitablewire bond thereto by end 18 of wire 16. After the formation of the bondof the end 18 of wire 16 to the end 15 of lead finger 14, theindependent clamp 24 and the bonding apparatus are actuated tosubstantially simultaneously remove the clamp 24 and the bondingapparatus 26 from the end 15 of the lead finger 14. Alternately, thebonding apparatus 26 is actuated to remove the apparatus from the bondlocation at the end 15 of the lead finger 14 either prior to or afterthe removal of the independent clamp 24 from a lead finger 14. Duringthe removal of the bonding apparatus 26 from the end 15 of the leadfinger 14, if used in addition to the independent clamp 24, aconventional clamp 22, if in contact with a lead finger 14, supplies thenecessary force to retain the finger 14 in position relative to otherlead fingers located around die 10, both bonded and unbonded. Aspreviously stated, it is not necessary for the independent clamp 24 toremain in contact with the end 15 of lead finger 14 during the removalof the bonding apparatus 26 therefrom. After the wire 16 has been bondedto the desired bond pad of die 10 and end 15 of lead finger 14, theprocess is repeated until all desired wire bonds between lead fingers 14and bond pads of die 10 are completed.

If desired to have additional clamping of the lead finger 14, either afixed clamp 22 and/or a second independent clamp 150 may be used withthe bonding apparatus 26. The second independent clamp 150 may beactuated and moved from the lead finger 14 with, before, or after theremoval of the bonding apparatus 26 from the lead finger 14.

It will be understood that the present invention may have changes,additions, deletions modifications, and sequence of operation which fallwithin the scope of the invention. For instance, the fixed clamp may beeliminated and a second independent clamp used in its place.

What is claimed is:
 1. A wire bonding method for bonding a portion of a wire to a portion of at least one lead finger of a lead frame using a movable clamp comprising: providing an independently movable clamp comprising a clamp movable in at least one x-axis direction, at least one y-axis direction, and at least one z-axis direction; positioning said independently movable clamp over a portion of said at least one lead finger for maintaining said at least one lead finger in position for attaching of at least said portion of said wire thereto; and providing an apparatus for bonding said portion of said wire to said portion of said at least one lead finger.
 2. The method of claim 1, further comprising: actuating said apparatus for bonding said portion of said wire to said at least one lead finger.
 3. The method of claim 2, further comprising: disengaging said independently movable clamp from said portion of said at least one lead finger before removal of said apparatus from said at least one lead finger.
 4. The method of claim 1, wherein said independently movable clamp comprises a resiliently mounted clamp.
 5. A wire bonding method for bonding a portion of a wire to a portion of a lead finger of a lead frame using a first clamp and an independently movable clamp comprising: positioning a first clamp over a portion of said lead finger for maintaining said lead finger in a position during said bonding said portion of said wire thereto, said first clamp comprising a clamp movable in at least one x-axis direction, at least one y-axis direction, and at least one z-axis direction; positioning an independent clamp over another portion of said lead finger for retaining said lead finger in said position during said bonding of said wire thereto; and providing an apparatus for bonding said portion of said wire to a portion of said lead finger.
 6. The method of claim 5, further comprising: actuating said apparatus for bonding said portion of said wire to a portion of said lead finger.
 7. The method of claim 6, further comprising: removing said independent clamp from engagement with said portion of said lead finger before removal of said apparatus from said lead finger.
 8. The method of claim 5, wherein said independent clamp comprises a resiliently mounted clamp.
 9. A wire bonding method for bonding at least a portion of a wire to a portion of a lead finger of a lead frame using a plurality of clamps comprising: positioning a first independent clamp over a portion of said lead finger for retaining said lead finger for bonding a portion of said wire thereto, said first independent clamp movable in at least one x-axis direction, at least one y-axis direction, and at least one z-axis direction; positioning a second independent clamp over another portion of said lead finger for restraining said lead finger in a position for said bonding of said wire thereto, said second independent clamp movable in said at least one x-axis direction, said at least one y-axis direction, and said at least one z-axis direction; and providing an apparatus for bonding said portion of said wire to a portion of said lead finger.
 10. The method of claim 9, further comprising: actuating said apparatus for bonding said portion of said wire to said portion of said lead finger.
 11. The method of claim 10, further comprising: removing said second independent clamp from said portion of said lead finger before removal of said apparatus from said lead finger.
 12. The method of claim 9, wherein said second independent clamp comprises a clamp for positioning between said first independent clamp and an end of said lead finger.
 13. The method of claim 9, wherein said first independent clamp and said second independent clamp each comprise an independently movable clamp with respect to each other clamp and said lead finger. 